Multibeam diffraction grating-based backlighting

ABSTRACT

Multibeam diffraction grating-based backlighting includes a light guide and a multibeam diffraction grating at a surface of the light guide. The light guide is configured to guide light from a light source. The multibeam diffraction grating is configured to couple out a portion of the guided light using diffractive coupling and to direct the diffractively coupled out portion away from the light guide as a plurality of light beams with different principal angular directions having directions corresponding to view directions of a multiview display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims the benefitof priority to pending U.S. patent application Ser. No. 14/908,523,filed Jan. 28, 2016, which claims benefit of priority to InternationalApplication No. PCT/US2013/052774, filed Jul. 30, 2013, the entirecontents of both of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

BACKGROUND

Electronic displays are a nearly ubiquitous medium for communicatinginformation to users of a wide variety of devices and products. Amongthe most commonly found electronic displays are the cathode ray tube(CRT), plasma display panels (PDP), liquid crystal displays (LCD),electroluminescent displays (EL), organic light emitting diode (OLED)and active matrix OLEDs (AMOLED) displays, electrophoretic displays (EP)and various displays that employ electromechanical or electrofluidiclight modulation (e.g., digital micromirror devices, electrowettingdisplays, etc.). In general, electronic displays may be categorized aseither active displays (i.e., displays that emit light) or passivedisplays (i.e., displays that modulate light provided by anothersource). Among the most obvious examples of active displays are CRTs,PDPs and OLEDs/AMOLEDs. Displays that are typically classified aspassive when considering emitted light are LCDs and EP displays. Passivedisplays, while often exhibiting attractive performance characteristicsincluding, but not limited to, inherently low power consumption, mayfind somewhat limited use in many practical applications given the lackof an ability to emit light.

To overcome the applicability limitations of passive displays associatedwith emitted light, many passive displays are coupled to an externallight source. The coupled light source may allow these otherwise passivedisplays to emit light and function substantially as an active display.Examples of such coupled light sources are backlights. Backlights arelight sources (often panel light sources) that are placed behind anotherwise passive display to illuminate the passive display. Forexample, a backlight may be coupled to an LCD or an EP display. Thebacklight emits light that passes through the LCD or the EP display. Thelight emitted is modulated by the LCD or the EP display and themodulated light is then emitted, in turn, from the LCD or the EPdisplay. Often backlights are configured to emit white light. Colorfilters are then used to transform the white light into various colorsused in the display. The color filters may be placed at an output of theLCD or the EP display (less common) or between the backlight and the LCDor the EP display, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features of examples in accordance with the principles describedherein may be more readily understood with reference to the followingdetailed description taken in conjunction with the accompanyingdrawings, where like reference numerals designate like structuralelements, and in which:

FIG. 1 illustrates graphical view of angular components {θ, ϕ} of alight beam having a particular principal angular direction, according toan example of the principles describe herein.

FIG. 2A illustrates a perspective view of a multibeam diffractiongrating-based backlight, according to an example consistent with theprinciples described herein.

FIG. 2B illustrates a cross sectional view of a multibeam diffractiongrating-based backlight, according to another example consistent withthe principles described herein.

FIG. 2C illustrates a cross sectional view of a multibeam diffractiongrating-based backlight, according to another example consistent withthe principles described herein.

FIG. 3 illustrates a plan view of a multibeam diffraction grating,according to another example consistent with the principles describedherein.

FIG. 4 illustrates a block diagram of a multiview electronic display,according to an example consistent with the principles described herein.

FIG. 5 illustrates a flow chart of a method of multiview displayoperation, according to an example consistent with the principlesdescribed herein.

Certain examples have other features that are one of in addition to andin lieu of the features illustrated in the above-referenced figures.These and other features are detailed below with reference to theabove-referenced figures.

DETAILED DESCRIPTION

Examples in accordance with the principles described herein providemultiview electronic display backlighting using multibeam diffractivecoupling. In particular, backlighting of an electronic display describedherein employs a multibeam diffraction grating. The multibeamdiffraction grating is used to couple light out of a light guide and todirect the coupled out light in a viewing direction of the multiviewelectronic display. The coupled out light directed in the viewingdirection by the multibeam diffraction grating includes a plurality oflight beams that have different principal angular directions from oneanother, according to various examples of the principles describedherein. In some examples, the light beams having the different principalangular directions (also referred to as ‘the differently directed lightbeams’) may be employed to display three-dimensional (3D) information.For example, the differently directed light beams produced by themultibeam diffraction grating may be modulated and serve as pixels of a‘glasses free’ multiview electronic display, for example.

According to various examples, the multibeam diffraction gratingproduces the plurality of light beams having a corresponding pluralityof different, spatially separated angles (i.e., different principalangular directions). In particular, each light beam produced by themultibeam diffraction grating has a principal angular direction given byangular components {θ, ϕ}. The angular component θ is referred to hereinas the ‘elevation component’ or ‘elevation angle’ of the light beam. Theangular component ϕ is referred to as the ‘azimuth component’ or‘azimuth angle’ of the light beam, herein. By definition, the elevationangle θ is an angle in a vertical plane (e.g., perpendicular to a planeof the multibeam diffraction grating) while the azimuth angle ϕ is anangle in a horizontal plane (e.g., parallel to the multibeam diffractiongrating plane). FIG. 1 illustrates the angular components {θ, ϕ} of alight beam 10 having a particular principal angular direction, accordingto an example of the principles describe herein. In addition, each lightbeam is emitted or emanates from a particular point, by definitionherein. That is, by definition, each light beam has a central rayassociated with a particular point of origin within the multibeamdiffraction grating. FIG. 1 also illustrates the light beam point oforigin P.

According to various examples, the elevation component θ of the lightbeam is related to, and in some examples determined by, a diffractionangle θ_(m) of the multibeam diffraction grating. In particular, theelevation component θ may be determined by the diffraction angle θ_(m)local to or at the point of origin P of the light beam, according tosome examples. The azimuth component ϕ of the light beam may bedetermined by an orientation or rotation of features of the multibeamdiffraction grating, according to various examples. In particular, anazimuth orientation angle ϕ_(f) of the features in a vicinity of thepoint of origin and relative to a propagation direction of lightincident on the multibeam diffraction grating may determine the azimuthcomponent ϕ of the light beam (e.g., ϕ=ϕ_(f)), according to someexamples. An example propagation direction of incident light isillustrated in FIG. 1 using a bold arrow.

According to various examples, characteristics of the multibeamdiffraction grating and the features thereof (i.e., ‘diffractivefeatures’) may be used to control one or both of the angulardirectionality of the light beams and a wavelength or color selectivityof the multibeam diffraction grating with respect to one or more of thelight beams. The characteristics that may be used to control the angulardirectionality and wavelength selectivity include, but are not limitedto, a grating length, a grating pitch (feature spacing), a shape of thefeatures, a size of the features (e.g., groove or ridge width), and anorientation of the grating. In some examples, the variouscharacteristics used for control may be characteristics that are localto a vicinity of the point of origin of a light beam.

Herein, a ‘diffraction grating’ is generally defined as a plurality offeatures (i.e., diffractive features) arranged to provide diffraction oflight incident on the diffraction grating. In some examples, theplurality of features may be arranged in a periodic or quasi-periodicmanner. For example, the diffraction grating may include a plurality offeatures (e.g., a plurality of grooves in a material surface) arrangedin a one-dimensional (1-D) array. In other examples, the diffractiongrating may be a two-dimensional (2-D) array of features. For example,the diffraction grating may be a 2-D array of bumps on a materialsurface.

As such, and by definition herein, the diffraction grating is astructure that provides diffraction of light incident on the diffractiongrating. If the light is incident on the diffraction grating from alight guide, the provided diffraction may result in, and thus bereferred to as, ‘diffractive coupling’ in that the diffraction gratingmay couple light out of the light guide by diffraction. The diffractiongrating also redirects or changes an angle of the light by diffraction(i.e., a diffractive angle). In particular, as a result of diffraction,light leaving the diffraction grating (i.e., diffracted light) generallyhas a different propagation direction than a propagation direction ofthe incident light. The change in the propagation direction of the lightby diffraction is referred to as ‘diffractive redirection’ herein.Hence, the diffraction grating may be understood to be a structureincluding diffractive features that diffractively redirects lightincident on the diffraction grating and, if the light is incident from alight guide, the diffraction grating may also diffractively couple outthe light from light guide.

Specifically herein, ‘diffractive coupling’ is defined as coupling of anelectromagnetic wave (e.g., light) across a boundary between twomaterials as a result of diffraction (e.g., by a diffraction grating).For example, a diffraction grating may be used to couple out lightpropagating in a light guide by diffractive coupling across a boundaryof the light guide. The diffractive coupling substantially overcomestotal internal reflection that guides the light within the light guideto couple out the light, for example. Similarly, ‘diffractiveredirection’ is the redirection or change in propagation direction oflight as a result of diffraction, by definition. Diffractive redirectionmay occur at the boundary between two materials if the diffractionoccurs at that boundary (e.g., the diffraction grating is located at theboundary).

Further by definition herein, the features of a diffraction grating arereferred to as ‘diffractive features’ and may be one or more of at, inand on a surface (e.g., a boundary between two materials). The surfacemay be a surface of a light guide, for example. The diffractive featuresmay include any of a variety of structures that diffract lightincluding, but not limited to, grooves, ridges, holes and bumps at, inor on the surface. For example, the multibeam diffraction grating mayinclude a plurality of parallel grooves in the material surface. Inanother example, the diffraction grating may include a plurality ofparallel ridges rising out of the material surface. The diffractivefeatures (e.g., grooves, ridges, holes, bumps, etc.) may have any of avariety of cross sectional shapes or profiles that provide diffractionincluding, but not limited to, one or more of a rectangular profile, atriangular profile and a saw tooth profile.

By definition herein, a ‘multibeam diffraction grating’ is a diffractiongrating that produces a plurality of light beams. In some examples, themultibeam diffraction grating may be or include a ‘chirped’ diffractiongrating. The light beams of the plurality produced by the multibeamdiffraction grating may have different principal angular directionsdenoted by the angular components {θ, ϕ}, as described above. Inparticular, according to various examples, each of the light beams mayhave a predetermined principal angular direction as a result ofdiffractive coupling and diffractive redirection of incident light bythe multibeam diffraction grating. For example, the multibeamdiffraction grating may produce eight (8) light beams in eight differentprincipal directions. According to various examples, the elevation angleθ of the light beam may be determined by a diffraction angle θ_(m) ofthe multibeam diffraction grating, while the azimuth angle ϕ may beassociated with an orientation or rotation of features of the multibeamdiffraction grating at a point of origin of the light beam relative to apropagation direction of light incident on the multibeam diffractiongrating, as described above.

According to various examples, a diffraction angle θ_(m) provided by alocally periodic, transmissive diffraction grating may be given byequation (1) as:

$\begin{matrix}{\theta_{m} = {\sin^{- 1}\left( {\frac{m\;\lambda}{d} - {{n \cdot \sin}\;\theta_{i}}} \right)}} & (1)\end{matrix}$where λ is a wavelength of the light, m is a diffraction order, d is adistance between features of the diffraction grating, θ_(i) is an angleof incidence of the light on the diffraction grating, and n is arefractive index of a material (e.g., a liquid crystal) on a side of thediffraction grating from which light is incident on the diffractiongrating (i.e., ‘light-incident’ side). Equation (1) assumes that arefractive index on a side of the diffraction grating opposite thelight-incident side has a refractive index of one. If the refractiveindex on the side opposite the light-incident side is not one, thenequation (1) may be modified accordingly. Herein, the plurality of lightbeams produced by the multibeam diffraction grating may all have thesame diffractive order m, according to various examples.

Further herein, a ‘light guide’ is defined as a structure that guideslight within the structure using total internal reflection. Inparticular, the light guide may include a core that is substantiallytransparent at an operational wavelength of the light guide. In someexamples, the term ‘light guide’ generally refers to a dielectricoptical waveguide that provides total internal reflection to guide lightat an interface between a dielectric material of the light guide and amaterial or medium that surrounds that light guide. By definition, acondition for total internal reflection is that a refractive index ofthe light guide is greater than a refractive index of a surroundingmedium adjacent to a surface of the light guide material. In someexamples, the light guide may include a coating in addition to orinstead of the aforementioned refractive index difference to furtherfacilitate the total internal reflection. The coating may be areflective coating, for example. According to various examples, thelight guide may be any of several light guides including, but notlimited to, one or both of a plate or slab guide and a strip guide.

Further herein, the term ‘plate’ when applied to a light guide as in a‘plate light guide’ is defined as a piecewise or differentially planarlayer or sheet. In particular, a plate light guide is defined as a lightguide configured to guide light in two substantially orthogonaldirections bounded by a top surface and a bottom surface of the lightguide. Further, by definition herein, the top and bottom surfaces areboth separated from one another and substantially parallel to oneanother in a differential sense. That is, within any differentiallysmall region of the plate light guide, the top and bottom surfaces aresubstantially parallel or co-planar. In some examples, a plate lightguide may be substantially flat (e.g., confined to a plane) and so theplate light guide is a planar light guide. In other examples, the platelight guide may be curved in one or two orthogonal dimensions. Forexample, the plate light guide may be curved in a single dimension toform a cylindrical shaped plate light guide. In various exampleshowever, any curvature has a radius of curvature sufficiently large toinsure that total internal reflection is maintained within the platelight guide to guide light.

Further still, as used herein, the article ‘a’ is intended to have itsordinary meaning in the patent arts, namely ‘one or more’. For example,‘a grating’ means one or more gratings and as such, ‘the grating’ means‘the grating(s)’ herein. Also, any reference herein to ‘top’, ‘bottom’,‘upper’, ‘lower’, ‘up’, ‘down’, ‘front’, back’, ‘left’ or ‘right’ is notintended to be a limitation herein. Herein, the term ‘about’ whenapplied to a value generally means within the tolerance range of theequipment used to produce the value, or in some examples, means plus orminus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwiseexpressly specified. Moreover, examples herein are intended to beillustrative only and are presented for discussion purposes and not byway of limitation.

FIG. 2A illustrates a perspective view of a multibeam diffractiongrating-based backlight 100, according to an example consistent with theprinciples described herein. FIG. 2B illustrates a cross sectional viewof a multibeam diffraction grating-based backlight 100, according toanother example consistent with the principles described herein. FIG. 2Cillustrates a cross sectional view of a multibeam diffractiongrating-based backlight 100, according to another example consistentwith the principles described herein. According to various examples, themultibeam diffraction grating-based backlight 100 is configured toprovide a plurality of light beams 102 directed away from the multibeamdiffraction grating-based backlight 100. In particular, the plurality oflight beams 102 is directed away from the multibeam diffractiongrating-based backlight 100 in different principal angular directions.In some examples, the plurality of light beams 102 forms a plurality ofpixels of an electronic display. In some examples, the electronicdisplay is a so-called ‘glasses free’ three-dimensional (3D) display(e.g., a multiview display). As such, the different principal angulardirections of the plurality of light beams may correspond to directionsof different views of a multiview display.

According to various examples, a light beam 102 of the plurality oflight beams provided by the multibeam diffraction grating-basedbacklight 100 is configured to have a different principal angulardirection from other light beams 102 of the plurality (e.g., see FIGS.2B and 2C). Further, the light beam 102 may have both a predetermineddirection (principal angular direction) and a relatively narrow angularspread. In some examples, the light beams 102 may be individuallymodulated (e.g., by a light valve as described below). The individualmodulation of the light beams 102 directed in different directions awayfrom the multibeam diffraction grating-based backlight 100 may beparticularly useful for multiview electronic display applications thatemploy relatively thick light valves, for example.

As illustrated in FIGS. 2A-2C, the multibeam diffraction grating-basedbacklight 100 includes a light guide 110. The light guide 110 isconfigured to guide light as guided light 104 (e.g., from a light source130). In some examples, the light guide 110 guides the guided light 104using total internal reflection. For example, the light guide 110 mayinclude a dielectric material configured as an optical waveguide. Thedielectric material may have a first refractive index that is greaterthan a second refractive index of a medium surrounding the dielectricoptical waveguide. The difference in refractive indices is configured tofacilitate total internal reflection of the guided light 104 accordingto one or more guided modes of the light guide 110, for example.

For example, the light guide 110 may be a slab or plate opticalwaveguide that is an extended, substantially planar sheet of opticallytransparent material (e.g., as illustrated in cross section in FIGS. 2Band 2C and from the top in FIG. 2A). The substantially planar sheet ofdielectric material is configured to guide the guided light 104 throughtotal internal reflection. In some examples, the light guide 110 mayinclude a cladding layer on at least a portion of a surface of the lightguide 110 (not illustrated). The cladding layer may be used to furtherfacilitate total internal reflection, for example.

In some examples, the guided light 104 may be coupled into an end of thelight guide 110 to propagate and be guided along a length of the lightguide 110. One or more of a lens, a mirror and a prism (notillustrated), for example may facilitate the coupling of the light intothe end or an edge of the light guide 110. According to variousexamples, the optically transparent material of the light guide 110 mayinclude or be made up of any of a variety of dielectric materialsincluding, but not limited to, various types of glass (e.g., silicaglass, alkali-aluminosilicate glass, borosilicate glass, etc.) andsubstantially optically transparent plastics or polymers (e.g.,poly(methyl methacrylate) or ‘acrylic glass’, polycarbonate, etc.).

As further illustrated in FIGS. 2B and 2C, the guided light 104 maypropagate along the light guide 110 in a generally horizontal direction.Propagation of the guided light 104 is illustrated from left to right inFIG. 2B as several bold horizontal arrows representing variouspropagating optical beams within the light guide 110. FIG. 2Cillustrates propagation of the guided light 104 from right to left, alsoas several horizontal arrows. The propagating optical beams mayrepresent plane waves of propagating light associated with one or moreof the optical modes of the light guide 110, for example. Thepropagating optical beams of the guided light 104 may propagate by‘bouncing’ or reflecting off of walls of the light guide 110 at aninterface between the material (e.g., dielectric) of the light guide 110and the surrounding medium due to total internal reflection, forexample.

According to various examples, the multibeam diffraction grating-basedbacklight 100 further includes a multibeam diffraction grating 120. Themultibeam diffraction grating 120 is located at a surface of the lightguide 110 and is configured to couple out a portion or portions of theguided light 104 from the light guide 110 by or using diffractivecoupling. In particular, the coupled out portion of the guided light 104is diffractively redirected away from the light guide surface as theplurality of light beams 102. As discussed above, each of the lightbeams 102 of the plurality have a different principal angular direction,according to various examples.

In particular, FIG. 2B illustrates the plurality of light beams 102 asconverging while FIG. 2C illustrates the light beams 102 of theplurality as diverging. Whether the light beams 102 are converging (FIG.2B) or diverging (FIG. 2C) may be determined by a direction of theguided light 104, for example. In some examples where the light beams102 are diverging, the diverging light beams 102 may appear to bediverging from a ‘virtual’ point (not illustrated) located some distancebelow or behind the multibeam diffraction grating 120. Similarly, theconverging light beams 102 may converge to a point (not illustrated)above or in front of the multibeam diffraction grating 120, according tosome examples.

According to various examples, the multibeam diffraction grating 120includes a plurality of diffractive features 122 that providediffraction. The provided diffraction is responsible for the diffractivecoupling of the guided light 104 out of the light guide 110. Forexample, the multibeam diffraction grating 120 may include one or bothof grooves in a surface of the light guide 110 and ridges protrudingfrom the light guide surface that serve as the diffractive features 122.The grooves and ridges may be arranged parallel to one another and, atleast at some point, perpendicular to a propagation direction of theguided light 104 that is to be coupled out by the multibeam diffractiongrating 120.

In some examples, the grooves and ridges may be etched, milled or moldedinto the surface or applied on the surface. As such, a material of themultibeam diffraction grating 120 may include a material of the lightguide 110. As illustrated in FIG. 2A, the multibeam diffraction grating120 includes substantially parallel grooves that penetrate the surfaceof the light guide 110. In other examples (not illustrated), themultibeam diffraction grating 120 may be a film or layer applied oraffixed to the light guide surface. The multibeam diffraction grating120 may be deposited on the light guide surface, for example.

The multibeam diffraction grating 120 may be arranged in a variety ofconfigurations at, on or in the surface of the light guide 110,according to various examples. For example, the multibeam diffractiongrating 120 may be a member of a plurality of gratings (e.g., multibeamdiffraction gratings) arranged in columns and rows across the lightguide surface. In another example, a plurality of multibeam diffractiongratings 120 may be arranged in groups (e.g., a group of three gratings,each grating in the group being associated with a different color oflight) and the groups may be arranged in rows and columns. In yetanother example, the plurality of multibeam diffraction gratings 120 maybe distributed substantially randomly across the surface of the lightguide 110.

According to some examples, the multibeam diffraction grating 120 mayinclude a chirped diffraction grating. By definition, the chirpeddiffraction grating is a diffraction grating exhibiting or having adiffraction spacing d of the diffractive features that varies across anextent or length of the chirped diffraction grating, as illustrated inFIGS. 2A-2C. Herein, the varying diffraction spacing d is referred to asa ‘chirp’. As a result, guided light 104 that is diffractively coupledout of the light guide 110 exits or is emitted from the chirpeddiffraction grating as the light beam 102 at different diffractionangles θ_(m) corresponding to different points of origin across thechirped diffraction grating, e.g., see equation (1) above. By virtue ofthe chirp, the chirped diffraction grating of the multibeam diffractiongrating 120 may produce the plurality of light beams 102 havingdifferent principal angular directions in terms of the elevationcomponent θ of the light beams 102.

In some examples, the chirped diffraction grating of the multibeamdiffraction grating 120 may have or exhibit a chirp of the diffractivespacing d that varies linearly with distance. As such, the chirpeddiffraction grating may be referred to as a ‘linearly chirped’diffraction grating. FIGS. 2B and 2C illustrates the multibeamdiffraction grating 120 as a linearly chirped diffraction grating, forexample. As illustrated, the diffractive features 122 are closertogether at a second end 120″ of the multibeam diffraction grating 120than at a first end 120′. Further, the diffractive spacing d of theillustrated diffractive features 122 varies linearly from the first end120′ to the second end 120″.

In some examples, light beams 102 produced by coupling light out of thelight guide 110 using the multibeam diffraction grating 120 includingthe chirped diffraction grating may converge (i.e., be converging lightbeams 102) when the guided light 104 propagates in a direction from thefirst end 120′ to the second end 120″ (e.g., as illustrated in FIG. 2B).Alternatively, diverging light beams 102 may be produced when the guidedlight 104 propagates from the second end 120″ to the first end 120′(e.g., as illustrated in FIG. 2C), according to other examples.

In another example (not illustrated), the chirped diffraction grating ofthe multibeam diffraction grating 120 may exhibit a non-linear chirp ofthe diffractive spacing d. Various non-linear chirps that may be used torealize the chirped diffraction grating include, but are not limited to,an exponential chirp, a logarithmic chirp and a chirp that varies inanother, substantially non-uniform or random but still monotonic manner.Non-monotonic chirps such as, but not limited to, a sinusoidal chirp anda triangle or sawtooth chirp, may also be employed.

According to some examples, the diffractive features 122 within themultibeam diffraction grating 120 may have varying orientations relativeto an incident direction of the guided light 104. In particular, anorientation of the diffractive features 122 at a first point within themultibeam diffraction grating 120 may differ from an orientation of thediffractive features 122 at another point. As described above, anazimuthal component of the principal angular direction {θ, ϕ} of thelight beam 102 may be determined by or correspond to the azimuthalorientation angle ϕ_(f) of the diffractive features 122 at a point oforigin of the light beam 102, according to some examples. As such, thevarying orientations of the diffractive features 122 within themultibeam diffraction grating 120 produce different light beams 102having different principal angular directions {θ, ϕ}, at least in termsof their respective azimuthal components ϕ.

In some examples, the multibeam diffraction grating 120 may includediffractive features 122 that are either curved or arranged in agenerally curved configuration. For example, the diffractive features122 may include one of curved grooves and curved ridges that are spacedapart from one another along radius of the curve. FIG. 2A illustratescurved diffractive features 122 as curved, spaced apart grooves, forexample. At different points along the curve of the diffractive feature122, an ‘underlying diffraction grating’ of the multibeam diffractiongrating 120 associated with the curved diffractive features 122 has adifferent azimuthal orientation angle ϕ_(f). In particular, at a givenpoint along the curved diffractive features 122 the curve has aparticular azimuthal orientation angle ϕ_(f) that generally differs fromanother point along the curved diffractive feature 122. Further, theparticular azimuthal orientation angle ϕ_(f) results in a correspondingazimuthal component of a principal angular direction {θ, ϕ} of a lightbeam 102 emitted from the given point. In some examples, the curve ofthe diffractive feature(s) (e.g., groove, ridge, etc.) may represent asection of a circle. The circle may be coplanar with the light guidesurface. In other examples, the curve may represent a section of anellipse or another curved shape, e.g., that is coplanar with the lightguide surface.

In other examples, the multibeam diffraction grating 120 may includediffractive features 122 that are ‘piecewise’ curved. In particular,while the diffractive feature may not describe a substantially smooth orcontinuous curve per se, at different points along the diffractivefeature within the multibeam diffraction grating 120, the diffractivefeature still may be oriented at different angles with respect to theincident direction of the guided light 104. For example, the diffractivefeature 122 may be a groove including a plurality of substantiallystraight segments, each segment having a different orientation than anadjacent segment. Together, the different angles of the segments mayapproximate a curve (e.g., a segment of a circle), according to variousexamples. See FIG. 3, which is described below. In yet other examples,the features may merely have different orientations relative to theincident direction of the guided light at different locations within themultibeam diffraction grating 120 without approximating a particularcurve (e.g., a circle or an ellipse).

In some examples, the multibeam diffraction grating 120 may include bothdifferently oriented diffractive features 122 and a chirp of thediffractive spacing d. In particular, both the orientation and thespacing d between the diffractive features 122 may vary at differentpoints within the multibeam diffraction grating 120. For example, themultibeam diffraction grating 120 may include a curved and chirpeddiffraction grating having grooves or ridges that are both curved andvary in spacing d as a function of a radius of the curve.

FIG. 2A illustrates the multibeam diffraction grating 120 includingdiffractive features 122 (e.g., grooves or ridges) that are both curvedand chirped (i.e., is a curved, chirped diffraction grating). An exampleincident direction of the guided light 104 is illustrated by a boldarrow in FIG. 2A. FIG. 2A also illustrates the plurality of emittedlight beams 102 provided by diffractive coupling as arrows pointing awayfrom the surface of the light guide 110. As illustrated, the light beams102 are emitted in a plurality of different principal angulardirections. In particular, different principal angular directions of theemitted light beams 102 are different in both azimuth and elevation, asillustrated. Nine separate light beams 102 are illustrated in FIG. 2A,by way of example and not limitation. As discussed above, the chirp ofthe diffractive features 122 may be substantially responsible for anelevation component of the different principal angular directions, whilethe curve of the diffractive features 122 may be substantiallyresponsible for the azimuthal component, according to some examples.

FIG. 3 illustrates a plan view of a multibeam diffraction grating 120,according to another example consistent with the principles describedherein. As illustrated, the multibeam diffraction grating 120 is on asurface of a light guide 110 and includes diffractive features 122 thatare both piece-wise curved and chirped. An example incident direction ofguided light 104 is illustrated by a bold arrow in FIG. 3.

Referring to again to FIGS. 2B and 2C, the multibeam diffractiongrating-based backlight 100 may further include the light source 130,according to some examples. The light source 130 may be configured toprovide light that, when coupled into the light guide 110, is the guidedlight 104. In various examples, the light source 130 may besubstantially any source of light including, but not limited to, one ormore of a light emitting diode (LED), a fluorescent light and a laser.In some examples, the light source 130 may produce a substantiallymonochromatic light having a narrowband spectrum denoted by a particularcolor. In particular, the color of the monochromatic light may be aprimary color of a particular color gamut or color model (e.g., ared-green-blue (RGB) color model). The light source 130 may be a red LEDand the monochromatic light is substantially the color red. The lightsource 130 may be a green LED and the monochromatic light issubstantially green in color. The light source 130 may be a blue LED andthe monochromatic light is substantially blue in color. In otherexamples, the light provided by the light source 130 has a substantiallybroadband spectrum. For example, the light produced by the light source130 may be white light. The light source 130 may be a fluorescent lightthat produces white light. In some examples, the guided light 104 may belight from the light source 130 that is coupled into an end or an edgeof the light guide 110. A lens (not illustrated) may facilitate couplingof light into the light guide 110 at the end or edge thereof, forexample.

In some examples, the multibeam diffraction grating-based backlight 100is substantially transparent. In particular, both of the light guide 110and the multibeam diffraction grating 120 may be optically transparentin a direction orthogonal to a direction of guided light propagation inthe light guide 110, according to some examples. Optical transparencymay allow objects on one side of the multibeam diffraction grating-basedbacklight 100 to be seen from an opposite side, for example.

According to some examples of the principles described herein, anelectronic display is provided. According to various examples, theelectronic display is configured to emit modulated light beams as pixelsof the electronic display. Further, in various examples, the emittedmodulated light beams may be preferentially directed toward a viewingdirection of the electronic display as a plurality of differentlydirected light beams. In some examples, the electronic display is amultiview electronic display (e.g., a glasses-free 3-D or multiviewelectronic display). Different ones of the modulated, differentlydirected light beams may correspond to different ‘views’ associated withthe multiview electronic display, according to various examples. Thedifferent ‘views’ may provide a ‘glasses free’ (e.g., autostereoscopic)representation of information being displayed by the multiviewelectronic display, for example.

FIG. 4 illustrates a block diagram of a multiview electronic display200, according to an example consistent with the principles describedherein. In particular, the multiview electronic display 200 illustratedin FIG. 4 is a multiview electronic display 200 (e.g., a ‘glasses free’3-D electronic display) configured to emit modulated light beams 202.The emitted, modulated light beams 202 are illustrated as diverging(e.g., as opposed to converging) in FIG. 4 by way of example and notlimitation.

The multiview electronic display 200 illustrated in FIG. 4 includes aplate light guide 210 configured to guide light as guided light. Theguided light in the plate light guide 210 is a source of the light thatbecomes the modulated light beams 202 emitted by the multiviewelectronic display 200. According to some examples, the plate lightguide 210 may be substantially similar to the light guide 110 describedabove with respect to multibeam diffraction grating-based backlight 100.For example, the plate light guide 210 may be a slab optical waveguidethat is a planar sheet of dielectric material configured to guide lightby total internal reflection.

The multiview electronic display 200 illustrated in FIG. 4 furtherincludes a multibeam diffraction grating 220. In some examples, themultibeam diffraction grating 220 may be substantially similar to themultibeam diffraction grating 120 of the multibeam diffractiongrating-based backlight 100, described above. In particular, themultibeam diffraction grating 220 is configured to couple out a portionof the guided light as a plurality of light beams 204. Further, themultibeam diffraction grating 220 is configured to direct the lightbeams 204 in a corresponding plurality of different principal angulardirections. In some examples, the multibeam diffraction grating 220includes a chirped diffraction grating. In some examples, diffractivefeatures (e.g., grooves, ridges, etc.) of the multibeam diffractiongrating 220 are curved diffractive features. In yet other examples, themultibeam diffraction grating 220 includes a chirped diffraction gratinghaving curved diffractive features. For example, the curved diffractivefeatures may include a ridge or a groove that is curved (i.e.,continuously curved or piece-wise curved) and a spacing between thecurved diffractive features that may vary as a function of distanceacross the multibeam diffraction grating 220.

In some examples, the multibeam diffraction grating 220 is a member of aplurality of diffraction gratings distributed across the plate lightguide. Diffraction gratings of the diffraction grating pluralityincluding the multibeam diffraction grating are arranged in rows andcolumns on the light guide surface, in some examples. As such, themultiview electronic display 200 may also comprise a plurality ofdiffraction gratings.

As illustrated in FIG. 4, the multiview electronic display 200 furtherincludes a light valve array 230. The light valve array 230 includes aplurality of light valves configured to modulate the differentlydirected light beams 204 of the plurality, according to variousexamples. In particular, the light valves of the light valve array 230modulate the differently directed light beams 204 to provide themodulated light beams 202 that are the pixels of the multiviewelectronic display 200. Moreover, different ones of the modulated,differently directed, light beams 202 may correspond to different viewsof the multiview electronic display 200. In various examples, differenttypes of light valves in the light valve array 230 may be employedincluding, but not limited to, liquid crystal light valves andelectrophoretic light valves. Dashed lines are used in FIG. 4 toemphasize modulation of the light beams 202.

According to various examples, the light valve array 230 employed in themultiview electronic display 200 may be relatively thick or equivalentlymay be spaced apart from the multibeam diffraction grating 220 by arelatively large distance. In some examples, the light valve array 230(e.g., using the liquid crystal light valves) may be spaced apart fromthe multibeam diffraction grating 220 or equivalently have a thicknessthat is greater than about 50 micrometers. In some examples, the lightvalve array 230 may be spaced apart from the multibeam diffractiongrating 220 or include a thickness that is greater than about 100micrometers. In yet other examples, the thickness or spacing may begreater than about 200 micrometers. A relatively thick light valve array230 or a light valve array 230 that is spaced apart from the multibeamdiffraction grating 220 may be employed since the multibeam diffractiongrating 220 provides light beams 204 directed in a plurality ofdifferent principal angular directions, according to various examples ofthe principles described herein. In some examples, the relatively thicklight valve array 230 may be commercially available (e.g., acommercially available liquid crystal light valve array).

In some examples (e.g., as illustrated in FIG. 4), the multiviewelectronic display 200 further includes a light source 240. The lightsource 240 is configured to provide light that propagates in the platelight guide 210 as the guided light. In particular, the guided light islight from the light source 240 that is coupled into the edge of theplate light guide 210, according to some examples. In some examples, thelight source 240 is substantially similar to the light source 130described above with respect to the multibeam diffraction grating-basedbacklight 100. For example, the light source 240 may include an LED of aparticular color (e.g., red, green, blue) to provide monochromatic lightor a broadband light source such as, but not limited to, a fluorescentlight to provide broadband light (e.g., white light).

According to some examples of the principles described herein, a methodof multiview display operation is provided. FIG. 5 illustrates a flowchart of a method 300 of multiview display operation, according to anexample consistent with the principles described herein. As illustrated,the method 300 of multiview display operation includes guiding 310 lightin a light guide as guided light. In some examples, the light guide andthe guided light may be substantially similar to the light guide 110 andguided light 104, described above with respect to the multibeamdiffraction grating-based backlight 100. In particular, in someexamples, the light guide may guide 310 the guided light according tototal internal reflection. Further, the light guide may be asubstantially planar dielectric optical waveguide (e.g., a plate lightguide), in some examples.

The method 300 of multiview display operation further includesdiffractively coupling out 320 a portion of the guided light using amultibeam diffraction grating. According to various examples, themultibeam diffraction grating is located at a surface of the lightguide. For example, the multibeam diffraction grating may be formed inthe surface of the light guide as grooves, ridges, etc. In otherexamples, the multibeam diffraction grating may include a film on thelight guide surface. In some examples, the multibeam diffraction gratingis substantially similar to the multibeam diffraction grating 120described above with respect to the multibeam diffraction grating-basedbacklight 100. In particular, the multibeam diffraction grating producesa plurality of light beams from the diffractively coupled out 320portion of the guided light. Further, each light beam of the light beamplurality propagates away from the light guide surface at a differentprincipal angular direction from other light beams of the light beamplurality. According to various examples, the different principalangular directions of the light beams of the light beam pluralitycollectively have principal angular directions corresponding todirections of different views of the multiview display.

In some examples, the method 300 of multiview display operation furtherincludes modulating 330 the light beams of the plurality of light beamsusing a corresponding plurality of light valves. In particular, theplurality of light beams may be modulated 330 by passing through orotherwise interacting with the corresponding plurality of light valves.The modulated light beams may form pixels of a three-dimensional (3D) ormultiview display, according to some examples. For example, themodulated light beams may provide a plurality of views of the multiviewdisplay (e.g., a glasses-free, 3D electronic display).

In some examples, the plurality of light valves used in modulating 330the plurality of light beams is substantially similar to the light valvearray 230 described above with respect to the multiview electronicdisplay 200. For example, the light valves may include liquid crystallight valves. In another example, the light valves may be another typeof light valve including, but not limited to, an electrowetting lightvalve and an electrophoretic light valve.

In some examples (not illustrated), the method 300 of multiview displayoperation further comprises providing the light to be guided in thelight guide using a light source coupled to an edge of the light guide.The light source may be substantially similar to the light source 130 ofthe above-described multibeam diffraction grating-based backlight 100,in some examples. Further, in some examples, the multibeam diffractiongrating may comprise a chirped diffraction grating having curveddiffractive features, a curve of the curved diffractive featuresdefining or at least partially defining the different principal angulardirection of light beams of the light beam plurality. In someembodiments, the multibeam diffraction grating is a member of aplurality of multibeam diffraction grating, multibeam diffractiongratings of the multibeam diffraction grating plurality being arrangedin rows and columns on the light guide surface.

Thus, there have been described examples of a multibeam diffractiongrating-based backlight, a multiview electronic display and a method ofmultiview display operation that employ multibeam diffraction gratingsto provide a plurality of differently directed light beams havingprincipal angular directions corresponding directions of different viewsof the multiview display. It should be understood that theabove-described examples are merely illustrative of some of the manyspecific examples that represent the principles described herein.Clearly, those skilled in the art can readily devise numerous otherarrangements without departing from the scope as defined by thefollowing claims.

What is claimed is:
 1. A multibeam diffraction grating-based backlightcomprising: a light guide configured to guide light from a light sourceas guided light; and a plurality of multibeam diffraction gratingsarranged across the light guide, each multibeam diffraction grating ofthe multibeam diffraction grating plurality being configured to coupleout a portion of the guided light using diffractive coupling, thediffractively coupled-out portion of the guided light being directedaway from a surface of the light guide as a plurality of light beams, alight beam of the light beam plurality having a different principalangular direction from other light beams of the light beam plurality,wherein different principal angular directions of the plurality of lightbeams correspond to directions of different views of a multiviewdisplay, wherein the multibeam diffraction grating comprises a chirpeddiffraction grating having curved diffractive features, a curve of thecurved diffractive features being configured to partially define thedifferent principal angular directions of the plurality of light beams.2. The multibeam diffraction grating-based backlight of claim 1, whereinmultibeam diffraction gratings of the multibeam diffraction gratingplurality are arranged in rows and columns on the surface of the lightguide.
 3. The multibeam diffraction grating-based backlight of claim 1,wherein the multibeam diffraction grating comprises a chirpeddiffraction grating.
 4. The multibeam diffraction grating-basedbacklight of claim 3, wherein the chirped diffraction grating is alinearly chirped diffraction grating.
 5. The multibeam diffractiongrating-based backlight of claim 1, wherein the multibeam diffractiongrating comprises one of curved grooves and curved ridges that arespaced apart from one another.
 6. The multibeam diffractiongrating-based backlight of claim 1, further comprising the light sourceat an edge of the light guide, the guided light being light from thelight source that is coupled into the edge of the light guide.
 7. Themultibeam diffraction grating-based backlight of claim 1, wherein thelight guide and the multibeam diffraction grating are substantiallytransparent in a direction orthogonal to a direction in which the lightis configured to be guided in the light guide.
 8. An electronic displaycomprising the multibeam diffraction grating-based backlight of claim 1,wherein the portion of the guided light is configured to bediffractively coupled out by the multibeam diffraction grating is lightcorresponding to a pixel of the electronic display, the electronicdisplay being the multiview display.
 9. The electronic display of claim8, further comprising a light valve configured to modulate the lightbeam of the plurality of light beams, the multibeam diffraction gratingbeing between the light valve and the surface of the light guide.
 10. Amultiview electronic display comprising: a plate light guide configuredto guide light from a light source as guided light; a plurality ofdiffraction gratings distributed across the plate light guide, amultibeam diffraction grating of the diffraction grating plurality beingconfigured to diffractively couple out a portion of the guided light asa plurality of light beams having a corresponding plurality of differentprincipal angular directions associated with different views of themultiview electronic display; and a light valve array configured tomodulate the light beams of the light beam plurality to provide aplurality of modulated light beams, wherein the plurality of modulatedlight beams having different principal angular directions representpixels of the different views of the multiview electronic display,different ones of the modulated light beams having directionscorresponding to different ones of the different views of the multiviewelectronic display.
 11. The multiview electronic display of claim 10,wherein diffraction gratings of the diffraction grating pluralityincluding the multibeam diffraction grating are arranged in rows andcolumns at a surface of the plate light guide.
 12. The multiviewelectronic display of claim 10, wherein the multibeam diffractiongrating comprises a chirped diffraction grating having curveddiffractive features.
 13. The multiview electronic display of claim 10,wherein the light valve array comprises a plurality of liquid crystallight valves.
 14. The multiview electronic display of claim 10, furthercomprising the light source, the guided light being light from the lightsource that is coupled into an edge of the plate light guide.
 15. Amethod of operating a multiview display, the method comprising: guidinglight in a light guide as guided light; and diffractively coupling out aportion of the guided light using a multibeam diffraction grating at asurface of the light guide to produce a plurality of light beams, eachlight beam of the light beam plurality propagating away from the lightguide surface at a different principal angular direction from otherlight beams of the light beam plurality, wherein different principalangular directions of light beams of the light beam pluralitycollectively have principal angular directions corresponding todirections of different views of the multiview display.
 16. The methodof operating a multiview display of claim 15, further comprisingmodulating the plurality of light beams using a corresponding pluralityof light valves, the modulated light beams forming pixels associatedwith the different views of the multiview display.
 17. The method ofoperating a multiview display of claim 15, wherein the multibeamdiffraction grating is a member of a plurality of multibeam diffractiongrating, multibeam diffraction gratings of the multibeam diffractiongrating plurality being arranged in rows and columns on the light guidesurface.
 18. The method of operating a multiview display of claim 15,wherein the multibeam diffraction grating comprises a chirpeddiffraction grating having curved diffractive features, a curve of thecurved diffractive features partially defining the different principalangular directions of light beams of the light beam plurality.
 19. Themethod of operating a multiview display of claim 15, further comprisingproviding the light to be guided in the light guide using a light sourcecoupled to an edge of the light guide.